US3811189A - Process for producing an improved cutting tool - Google Patents

Abstract

The sharpened edge of a cutting implement such as a razor blade is modified by depositing a layer of dielectric material on the cutting edge and then depositing a layer of electrically conductive material on the dielectric layer and then subjecting the cutting edge to DC ion bombardment so that a portion of the deposited electrically conductive material is removed and the dielectric material is exposed at the tip of the implement.

Description

[11] 3,811,189 May 21, 1974 United States Patent 1191 Sastri 3,632,494 1/1972 Herte et 3,743,551 7/1973 Sanderson 3,754,329

8/1973 Lane....................... 30/346.53

Aiyaswami S. Sastri, Stow, Mass.

FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee: The G'llete companyBostonMass' 1,030,401 5/1966 Great Britain,.................. 30/346.55 [22] Filed:

Mar. 19, 1973 Primary Examiner-Al Lawrence Smith Assistant Examiner-J. C. Peters [21] Appl. N0.: 342,754

Related US. Application Data [62] Division of Ser. No. 161

,159, July 9, 1971, Pat. No.

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3 345 202 10/1967 Kiss et al. 30/346.53 x 3,480,483 11/1969 Wilkinson1.......,................ 204/192 5 Claims, 3 Drawing Figures PATENTEDHAYZI 1914 FIG i FIG 3 FIG 2 PROCESS FOR PRODUCING AN IMPROVED CUTTING TOOL This application is a division of Ser. No. 161,159, filed July 9, 1971, entitled Process for Producing an Improved Cutting Tool," now US. Pat. No. 3,761,373.

SUMMARY OF INVENTION This invention relates to processes for producing an extremely sharp and durable cutting edge on a razor blade or similar cutting tool, and to improved cutting tools.

The forming of the cutting edges of razor blades by mass production techniques conventionally involves a series of abrading operations (grinding and honing) to produce the desired sharp and durable shaving edge. Each abrading operation forms a facet on the blade edge being sharpened, which facet is modified by subsequent abrading operations of increasing fineness. In general, the blade edge configuration is a wedge shape, the included solid angle of which is typically 2030. The faces or sides of such cutting edges may extend back from the ultimate edge a distance up to as much as 0.1 inch or even more. Each face need not be a single uninterrupted continuous surface or facet, but may consist of two or more facets formed by successive grinding or honing operations and intersecting each other along zones generally parallel to the ultimate edge. The final facet, i.e., the facet immediately adjacent the ultimate edge, has a width as low as 7.5 microns or even less compared with the diameter-of beard hair which averages about 100 to 125 microns. Through shave test evaluation and measurement of the geometry of such sharpened cutting edges, it has been found that the cutting edge should have an average tip radius of less than 500 Angstroms. A thin adherent layer of a corrosion resistant metal is often applied to the cutting edge of the blade. Further, a shave facilitating layer of polymeric material is also frequently applied to the blade edge. These layers must have adhesion compatability so that they remain firmly adhered to one another and to the substrate throughout the life of the cutting tool and not adversely affect the edge geometry.

It is a general object of this invention to provide novel and improved cutting implements, the cutting edges of which have improved mechanical properties.

Another object of the invention is to provide novel and improved processes for producing improved cutting tools.

A further object of the invention is to provide novel and improved razor blades which possess superior shaving properties.

In accordance with the invention, the edge geometry of a cutting implement such as a razor blade is modified by a process which includes the steps of forming a cutting edge of dielectric material, depositing a layer of electrically conductive material on said dielectric material, and then subjecting the composite cutting edge to a DC ion bombardment step so that a portion of the deposited electrically conductive material is removed so that the dielectric material is exposed at the ultimate tip.

In particular embodiments, the cutting edge is formed in a metal substrate by a suitable procedure such as grinding, honing, stropping, chemical etching, electrolytic sharpening, or forming with an appropriately shaped die; and then the edge is subjected to two successive strengthening material deposition steps, the first step depositing a layer of dielectric material and the second step depositing the layer of electrically conductive material. Preferably the layers are deposited by sputtering on a multiplicity of blade elements while the blade edges are disposed in parallel alignment with one another and in a plane parallel to a target member spaced from the blade edges. A planar target member is used in one embodiment while a cylindrical target rod is used in another embodiment.

A razor blade in accordance with the invention has an average tip radius of less than 500 Angstroms, the exposed tip material is a dielectric, such as A1 0 and added strengthening metal, such as chromium or a chrome-platinum alloy, is on the flanks of the cutting edge. Such razor blades exhibit excellent shaving characteristics and have a long shaving life. A wide range of blade substrate materials may be used, specific razor blade steel compositions with which the invention may be practiced including the following:

COMPOSITION IN C Cr Mo Si Ni Other objects, features and advantages of the invention will be seen as the following description of particular embodiments progresses, in conjunction with the DESCRIPTION OF PARTICULAR EMBODIMENT Diagrammatically shown in FIG. 1 is a sputtering apparatus which includes a stainless steel chamber 10 having wall structure 12 and a base 14 in which is formed a port 16 which is coupled to a suitable vacuum system (not shown). Mounted in chamber 10 is a support 18 on which is disposed a stack of razor blades 20 and support structures 22, 24 for target member 26 of dielectric material and target 28 of electrically conductive material. Support structures 18, 22 and 24 are electrically isolated from chamber 10 and electrical connections are provided to connect blade stack 20 and targets 26, 28 to appropriate energizing apparatus 30, 32, 34. It will be understood that this is a diagrammatic showing of suitable apparatus. In one embodiment the targets 26, 28 are horizontally disposed discs, each 6 inches in diameter and one-quarter inch thick; and 4 U2 inch long stack of blades 20 is placed on a 5 inch diameter aluminum support disc 18 disposed parallel to target discs 26, 28. Disc 18 is movable between a first position aligned with target 26 and a second position aligned with target 28. A coil of razor blade strip may be similarly positioned on such a support with its sharpened edges defining a plane exposed to parallel to targets 26, 28. In another embodiment, target rod that has an exposed length of 29 inches and is 1 1/4 inches in diameter is employed. Suitable coolant is circulated through the rod for cooling purposes. A series of stacks of razor blades (either in coil form or in twelve inch long axial extending stacks) are disposed about, the target rod at equal distances therefrom.

The geometry of the edge of a typical razor blade of commercial quality sharpened by conventional abrading techniques is shown in F IG. 2 at a magnification of about 100,000 times. The tip 40 has a radius that is typically in the range of 125-500 Angstroms, a typical average radius (the average of radius measurements taken at 5 to points along the length of the blade edge) being about 2 50 Angstr0nts. The Wlilank width (at a distance of 1,000 Angstroms fr om the u ltim ate edge 40) is typically in the range of 1,200 to 1,400

Angstroms. The W2 width (at a distance of 2,000 Ang- 1 strorns from the tip 40) is about 2,100 Angstroms; the W4 width (at a distance of 4,000 Angstroms from the tip 40) is about 3,200 Angstroms; the W6 width (at a distance of 6,000 Angstroms) is about 4,100 Angstroms; and the W8 width (at a distance of 8,000 Angstroms from the tip) is about 5,100 Angstroms.

These measurements were made by a high resolution electron microscopy technique in which a magnified image of a blade edge profile (silhouette) is photographed. The blades are cleaned by immersion in trichloroethylene; subjection to ultrasonic cleaning for 2 minutes; rinsing in a mixture of one-half acetone and one-half methanol; cleaned in warm air; and then demagnetized in a solenoid coil. A blade specimen in the order of one square millimeter in size with four sides, one of which is the original sharpened razor blade edge, is obtained by abruptly snapping the blade with the help of a suitable instrument such as a watchmakers plier. The blade may be snapped in air or if the blade will-not break readily in liquid nitrogen (at a temperature below the ductile to brittle transition value).

A 100 KV RCA EMU4 electron microscope is used with a standard air lock specimen holder modified to accommodate the small blade edge fragment. The microscope was fitted with a liquid nitrogen cooled bafile valve to reduce contamination during photography. The blade edge profile is held in the path of the electron beam so that a shadow image of the ultimate tip is cast on the final viewing screen. The magnification of the final image is controlled by the strength of the intermediate lens current and the focusing is achieved with control of the objective lens current. The microscope magnification was calibrated in terms of focusing lens current.

The tip radius of the resulting photomicrograph was measured by fitting 90 arcs of circles to the tip profile and selecting as the tip radius that edge profile that best fits the profile of the photomicrograph. The point to point resolution of the microscope is in the order of 5 Angstroms. The variation and average radius of a large number of edges from a particular batch of blades using this technique was within i 12.5 Angstroms. The W1, W2 and other dimensions are similarly measured from the photomicrograph.

in operation of the apparatus shown in F 1G. 1, sharpened blades 20 are disposed in a stack with their sharpened edges aligned and are placed in chamber 10 on support 18. The chamber is evacuated and the blade edges are subjected to ion bombardment, for example by a glow discharge maintained in argon at a pressure of ten microns to modify the edge geometry as generally indicated byline 42 in FIG. 2 and specifically to reduce the tip radius, a typical radius reduction being about Angstroms. The chamber is again evacuated and argon at a pressure of 5-8 microns is placed in the chamber. With the blade stacks and chamber grounded, an RF potential is applied to dielectric target 26 and argon ions are produced which bombard target 26 and release atoms of the target material. The released atoms of dielectric material are deposited on exposed surfaces, including the sharpened blade edges. This layer is applied uniformly to the thickness of less than 500 Angstroms. The support 18 is then aligned with target 28 and an RF potential applied to that target to cause deposition of an electrically conductive layer on the dielectric layer. The RF power supply is then disconnected from the target 28and the blades are subjected to DC ion bombardment. which removes electrically conductive but not dielectric material, more material being removed from the tip region of the blades than the flanks. The resulting blades have a cutting edge geometry of the nature diagrammatically indicated in FlG. 3 in which the exposed tip 44 is dielectric material and its average radius is about-250 Angstroms and two layers 46, 48 are on the flanks at the W6 dimension.

As a specific example, a 4 1/2-inch long stack of stainless steel razor blades having the following composition:

carbon 0.54-0.62% chromium 13.5-14.S% manganese 0.20-0.S0% silicon 0.20O.50% phosphorus, max. 0.025% sulphur, max. 0.020% nickel, max. 0.50% max. iron remainder and sharpened to the edge geometry as indicated in FIG. 2, were placed on a 5 inch diameter aluminum disc support 18 in an RF sputtering unit. Two targets were employed, an A1 0 target 26, and a Cr Pt target 28. The A1 0 target 26 was a sintered compact disc six inches in diameter and 1/4 inch thick, and the Cr Pt target 28 was a pure chromium disc 6 inches in diameter and 1/4 inch thick that had squares of pure platinum foil one centimeter on a side and 0.002 inch thick spot welded on its surface. The foil squares were spaced on the surface so that 23 percent of the chromium surface was covered with platinum. The target surfaces were disposed parallel to the sharpened blade edges at a distance of 2 112 inches from those edges.

Pressure in the vacuum chamber 10 was reduced to 0.1 micron of mercury and then pure argon gas was bled into the chamber to a pressure of ten microns of mercury. The aluminum support disc 18 was then connected to a DC source of power and with the chamber 10 grounded the blade edges were subjected to ion bombardment at a voltage of 1,800 volts and a current of 35 milliamperes for seven minutes. The targets 26,

28 were covered by metal shields during this step. A

13.56 magahertz RF source was connected to A1 0 target 26 and that target was sputtered for thirty minutes while maintaining ten microns of mercury pressure or argon gas in the chamber. The shield was then removed from between the blades 20 and the target 26 and 0.4 kilowatts of power (with a DC negative bias of about 3,400 volts and a superimposed RF signal of 5 about 4,500 volts peak to peak) was applied for 1 minutes while maintaining argon at 10 micrions pressure. The edges of the blades facing target 26 received an aluminum oxide layer 46 to a thickness of about 250 Angstroms. Application of RF power was then terminated and support 18 was aligned with the Cr Pt target 28. The Cr Pt target 28 was connected to the RF source and cleaned for five minutes and then a layer 48 of chromium-platinum alloy 250 Angstroms in thickness was deposited by application of 0.4 kilowatts of power for 75 seconds. The blade stack was then connected to the DC source and subjected to ion bombardment for seven minutes at 1,800 volts ata current of 100 milliamperes to remove the chromium-platinum film from the tip region but not the flank region of the blades to provide a blade edge geometry as shown in FIG. 3. The resulting blades have an average tip radius of 250 Angstroms, an average W1 dimension of about 1,400 Angstroms, a W2 dimension of about 2,500 Angstroms, a W4 dimension of about 4,000 Angstroms, and a W6 dimension of about 5,150 Angstroms. A coating of polytetrafluoroethylene telomer was then applied to the edges of the blades in accordance with the teaching in US. Pat. No. 3,518,110. This processing involved heating the blades in an argon environment and provided on cutting edges of the razor blades an adherent coating of solid PTFE. These blades exhibited excellent shaving properties and long shaving life.

It will be understood that a variety of dielectric materials including other metal oxides may be used for the dielectric layer 46 and that other metals and metal alloys may be used for the electrically conductive layer 48. lon bombardment between the application of the dielectric and conductive layers is optional. For exam- 6 ple, such ion bombardment may be desirable when the process is employed with separate deposition chambers with a single target in each chamber.

The invention provides an improved cutting implement such as a razor blade in which the tip radius of the implement is within the optimum range for cutting effectiveness, the exposed tip is of dielectric material and substantial amounts of edge strengthening materials have been added to the flanks of the cutting edge.

While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention.

What is claimed is:

l. A cutting implement having an average tip radius of less than 500 Angstroms, said cutting implement comprising a metal substrate having a cutting edge with a tip radius of less than 500 Angstroms, a layer of dielectric material on the tip and flanks of said cutting edge, the thickness of said dielectric layer being in the range of about -300 Angstroms, the exposed tip of said cutting implement being of said dielectric material and a layer of electrically conductive strengthening metal on said dielectric material on the flanks of said cutting edge.

7 2. The cutting implement as claimed in claim 1 wherein said dielectric material is a metal oxide.

3. The cutting implement as claimed in claim 2 wherein said metal oxide is aluminum oxide.

4. The cutting implement as claimed in claim 3 wherein said electrically conductive layer includes chromium.

5. The cutting implement as claimed in claim 1 wherein said cutting implement is a razor blade.

Claims (5)

1. A cutting implement having an average tip radius of less than 500 Angstroms, said cutting implement comprising a metal substrate having a cutting edge with a tip radius of less than 500 Angstroms, a layer of dielectric material on the tip and flanks of said cutting edge, the thickness of said dielectric layer being in the range of about 100-300 Angstroms, the exposed tip of said cutting implement being of said dielectric material and a layer of electrically conductive strengthening metal on said dielectric material on the flanks of said cutting edge.

2. The cutting implement as claimed in claim 1 wherein said dielectric material is a metal oxide.

3. The cutting implement as claimed in claim 2 wherein said metal oxide is aluminum oxide.

4. The cutting implement as claimed in claim 3 wherein said electrically conductive layer includes chromium.

5. The cutting implement as claimed in claim 1 wherein said cutting implement is a razor blade.

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